In recent years, an internal combustion engine fitted with a combustion pressure detection device for detecting a pressure inside a combustion chamber has been known. In such an internal combustion engine, it is necessary to suppress leakage of combustion gas from an fitting portion of the combustion pressure detection device in the combustion chamber, or to prevent inflow of the combustion gas to the combustion pressure detection device.
For example, a combustion pressure detection device described in Patent Document 1 includes a diaphragm at a front end part of a main body formed in a cylindrical shape, and in a combustion pressure sensor that is provided by being inserted into an insertion hole provided at a combustion chamber wall so as to be able to detect combustion pressure in a combustion chamber acting via the diaphragm by a sensor part configured with a piezoelectric element arranged at the back of the diaphragm, a gas-sealing part protruding in the radial direction is provided at the front end part of the main body thereof, and the gas-sealing part is configured to face an inner wall surface of the insertion hole in the radial direction so as to be brought into press contact therewith.